Additive manufacturing, rapid manufacturing or rapid prototyping methods for producing three-dimensional components are well known in the art (see for example U.S. Pat. No. 4,863,538—Deckard). There are various known methods of additive manufacturing including consolidation of powder materials and curing of polymeric resins (Stereolithography-SLA). SLM and SLS manufacturing methods involve a layer-by-layer consolidation of powder material using a focused energy beam, such as a laser beam or an electron beam.
In a typical selective SLS or SLM process, a thin layer of powder is deposited over a build area or powder bed within a SLS or SLM apparatus. A focused laser beam is scanned across portions of the powder layer that correspond to a cross-section of the three-dimensional article being constructed such that the powder at the points where the laser scans is consolidated either by sintering or by fusion. The cross-section is typically generated from a 3-D description of the component generated by scanning an original component or from computer-aided design (CAD) data.
After consolidation of a layer, the build surface is lowered by the thickness of the newly consolidated layer and a further layer of powder is spread over the surface. Again, the surface is irradiated with a laser beam in portions of the layer that correspond to a cross-section of the three-dimensional article, the newly consolidated layer being joined to the initial consolidated layer. This process is repeated until the component is completed.
When operating an additive manufacturing apparatus as described above a high powered laser heats the powder beyond its melting point resulting in formation of metal vapour in the atmosphere above the build surface. This metal vapour subsequently condenses forming powders with extremely small diameter e.g. diameters below 1 micron. At these diameters powders of most material types, particularly metals such as titanium, are highly reactive and liable to spontaneously combust on contact with air. The condensates usually appear as a “smoke” in the region above the build surface (build chamber) and some of this smoke is removed from the build chamber by a flow of inert gas through the build chamber.
Although it is relatively easy to trap such fine condensates within a filter element arranged in-line with the gas flow (where the collected residue resembles soot) there is a significant safety problem with the reactivity of the condensates. When changing filters, extreme care must be taken to prevent fires igniting within the filters on contact with air. Although a fire within a filter is a small fire, any fire near an apparatus containing metal powder or in a facility containing metal powder may act as to ignite a much larger and potentially serious fire. Therefore, deposits need to be treated with great care and collected in a safe manner in an inert atmosphere before being neutralised.
A prior art method of removing a used filter element from a filter assembly on an additive manufacturing machine involves the withdrawal of the filter element into a polythene bag associated with the filter assembly. The bag is then manually tied at two points on its length between the removed filter element and the filter assembly and cut between these two sealed points to remove the filter element without exposure to air. The bag containing the filter element is then placed in an airtight container and removed from the site to be disposed of. This prior art method leaves much room for human error, for example in safe sealing of the bag as it is removed.